On the distribution of Gonionemus vertens A. Agassiz (Hydrozoa, Limnomedusae), a new species in the eelgrass beds of Lake Grevelingen (S.W. Netherlands)

On the distribution of Gonionemus vertens A. Agassiz (Hydrozoa, Limnomedusae), a new species in the eelgrass beds of Lake Grevelingen (S.W. Netherlands)